Multiple Protocol Label Switching (MPLS) networks use a switching technique whereby packets may be routed across a network. The packets transmitted across the MPLS network may take a variety of forms and may include a label. The label may be a fixed value, for example, an integer. The labels may be used to indicate the destination of the packet.
The MPLS network may include a plurality of nodes. The nodes may include Label Edge Routers (LERs) where information enters the network (“ingress nodes”) and where information leaves the network (“egress nodes”). The LER may add a label to the head of the packet to indicate the destination of the packet. The LERs may ignore other information in the packet, for example, Internet protocol (IP) addresses and ATM VCI/VPI information.
The LER may be used in a MPLS network as the boundary between Layer 3 forwarding and MPLS forwarding. The LER may include functionality to add a label to an unlabeled packet (“an ingress LER”) and remove labels from the packet (“an egress LER”).
Label Switching Routers (“LSRs”) may be used to route the packets between LERs. The LSRs may examine the label in a packet to determine the destination of the packet. In one example, the label may indicate an index in a table (stored in the switching node) and may be used to determine the outgoing link to which the packet may be forwarded. The table may be stored in a memory at the switching node, for example.
The LSRs may assign a new label and forward the packet on the link. Each label may have significance only locally. In other words, the packets may be forwarded hop-by-hop across the MPLS network. The label may indicate each hop rather than the entire end-to-end path from the source to the destination.